Combustion apparatus for operation in fast-moving air streams



2,66 7,033 APPARATUS FOR OPERATION REAMS 5 Sheets-Sheet l P. F. ASHWOOD COMBUSTION IN FAST-MOVING AIR ST Jan. 26, 1954 Flled Dec 25 1947 Jan. 26, 1954 F. ASHWOOD COMBUSTION AP 2,667,033 PARATUS FOR OPERATION IN FAST-MOVING AIR STREAMS 3 Sheets-Sheet 2 Filed Dec. 23, 1947 INVENTOR.

2,667,033 TION 5 sheets-sheet s INVENTOR.

' ATTORNEYS Jam 1954 P. F. ASHWOOD COMBUSTION APPARATUS FOR OPERA IN FAST-MOVING AIR STREAMS Filed D80. 23, 1947 Pem'gedw'ckmaod" Patented Jan. 26, 1954 UNITED STATES P OFFICE COMBUSTION APPARATUS FOR OPERATION IN FAST-MOVING AIR- STREAMS Peter Frederick Ashwood,

assignor to Power Jets ment) Limited, London,

company Old Coulsdon, England, Research and Develop- England, a British Application December 23, 1947, Serial No. 793,375

Claims priority, application Great Britain January 9, 1947 4 Claims.

to have its maximum utility in connection with combustion apparatus in which special problems arise due to the necessity for supporting continuous combustion by means of a fast moving gaseous current involving a large mass iiow, as for example, in gas turbines or other jet propulsion power units and in gas turbines for other purposes. The description fast moving as applied to a combustion-supporting gas flow is used hereing in unit time/cross sectional area of flow path, is substantially higher than the speed of flame propagation in the fuel/gas mixture concerned. For hydrocarbons fuels burning in air the speed of flame propagation is considered as being of the order of 1 foot per second at atmospheric temperature; the invention, on the other hand, is especially applicable to combustion appa ratus for gas turbines or/and jet propulsion power units in which the speed of the air current in its general direction of flow past a combustion zone, calculated on the basis indicated, might be of an order as low as or as high as 300 feet per second or even more, depending on the design.

The object of the invention stated in general terms is to enable stable combustion to be supported not only by a fast moving gas flow but also with high air/fuel ratios and with high rates of fuel injection and low pressure loss, all of which are requirements further arising in connection with gas turbines and jet propulsion units; the invention in fact owes its origin to the needs of such units and it is primarily to these that its application is contemplated, although of course it may be applied in other cases Where comparable problems arise.

In combustion systems employing velocities of the order indicated, the gas flow must de difiused or reduced in velocity before combustion can be eifectively maintained. It has accordingly been the practice to employ a diffuser section of substantial length in series with the inlet to the apparatus and the combustion zone; which has necessarily involved undue length and Weight of Cl. Bil-39.37)

is quite disproportionate. It is accordingly a further object of the invention to reduce the overall length required for the diffusion and combustion processes as compared with known combustion systems. Equally however, the invention may be applied to the reduction of length of a combustion system even where there is no compressor.

The invention may conveniently be considered as having two principal aspects which, whilst being closely inter-related,

bustion.

Considered in its first aspect the invention proposes to employ upstream injection of fuel into the upstream limiting region of the combustion for the combustion zone lationship in the general flow, the diifusion bustion chamber at its upstream end to direct 1 a part only of a gas flow in the duct at one or more points into a radially inner part of a fuel jet or spray directed upstream into the upstream limiting region of the combustion zone.

Preferably also, in regard :to the second aspect of the invention, the diffusion vor flow velocity reducing system through which air is by-passed around the upstream end of the combustion zone is afforded between the combustion chamberand the ducting, preferably by mutually relating the internal :form of the ducting and the external form :of the chamber defining the combustion zone so as to form a diffusion passage between said ducting and chamber having :itsentryat the upstream limit of said chamber and its outlet at a :downstream region of the combustion zone therein.

According to .a further feature of the inven- :tion the division of the gas flow is such that only :a minor proportion of the gas flow is supplied to the upstream limiting region of the combustionizonefithe major proportion of the flow beii g :by-rpassed and having itsfirstentryito the cham- .ber as a major inflow ina .zone of the combustion chamber downstream \of its upstream limiting region but .yetstillina region of upstream fuel injection thereto. The intention here is .to pro- :vide a .primary combustion zone .at the upstream end of the combustion chamber in whichamajor .part of the combustion takes place. The comi bustion chamber, however, preferably extends downstream for a sufficiently substantial distance :to allow combustion to be substantially completed within it, the wall of the combustion chamber :being ported at successive :zones spaced in the direction of flow in order .to admit :seciondary combustion gas inflows and diluent and mixing inflows.

A particular constructional form which maybe regarded as representing a more limited iaspect of the invention is that arising from the application of .a combustion apparatus according .to the invention to agas turbine unit :of the kind comprising a coaxial compressor and turbine .and having .its combustion apparatus embodied therein .as an annular :series .of combustion chambers contained in ducting annularly dis- ,posedcoaxially with the compressor :and turbine .and conducting the output of the former to the :latter. the combustion chambers, by making use .of :the feature of the invention which provides ior an overlap between the diffusion system of the combustion apparatus and its combustion zone, may be made to lie close up "to the compressor outlet so that virtually no additional length is required fordiffusion of thecompressor output after leaving the compressor proper. It will be appreciated, of course, that in such acase either the gas :ductingmay be an annular air-casing containing all the combustion chambers, or there may be a separate air casing for .eachcombustion chamber.

Examples of construction .in accordance with the invention are illustrated in the drawings of which:

In such a .case the upstream ends of ducting 'which'receives a plurality of flame tubes is annular; and,

Figure 4 is a view in section taken along the :line 4-4.ofiEig11rel3.

Referringto the drawings, the combustion apparatus comprises an air duct I having at its upstream end a flange 2 by which it is intended that it should be secured direct to the outlet from a compressor in a gas turbine of conventional type. A'fragment of :a compressor of conventional type :is shown in Figure 2 and is indicated by the reference character t2a. The .opposite or downstream end of the 'air'duct'hasa'flange 3 bywhich 'it'is intended to bersecured to the nozzle housing of a turbine. A fragment of a conventional turbine nozzle housing is indicated at 3a in acter is of course well know and so is not iconsidered to require further description. Within the air 'duct .is a combustion chamber in the :form of a flame tube 4having its upstream end formed by a conical bafiie-B with :its -.apex.;point ing downstream. Inside the .flame tube a fuel nozzlerB is arranged in alignment with .the apex .of the conical baffle 15 :to inject :fuel in an .upstream direction into the upstream limitmg region of the frame tube :4, that .is at the :apex of the cone 5,.as indicated in Figure 1. The conical baffle is imounted on,afrustoconical part 1 of the flame tube 4 :whichformsin effect zan cutward and downstream extension from the base :of the cone, but also forms a lip 8 extending some distance upstream beyond the base 'of the cone to "form an aperture d dimensioned to admit a desired proportion of the total air flow to the interior of the cone, the "proportion in the preferred cases illustrated being a .minor proportion which is in the nature of a :pilot'flow. The flame tube is so arranged that the plane of its entry 9 vrisrclose up to that of the flange .2. The air duct, except for .a short cylindrical part immediately downstream .of the compressor :at 10, also increases'in diameter in the downstream direction so as to "form with the f'rusto-conical nose .7 :of the flame tube an annular space 4 l of increasing .cross sectional area in the downstream direction designed as a diffusion passage suitable 'for (the velocity conditions involved. It will be 12.13- preciated "that although the walls .of the annulus :H in the drawings :do not diverge appreciably, the progressive increase in the downstream direction of its mean radius is sufficient to afford an increasing cross-section. :From the downstream end of the annular .difE-usion passage .cH so formed both .the'flame tube and the air duct are of cylindrical form fonsome distance, theair duct terminating at its downstream --end in a tapering section J2 leading to the turbine inlet. Upstream .of this region the flame tube has an outwardly flared frusto-conical portion 13 which increases in diameter nearly to that of the .casing, the downstream end of this part being radially located by spaced peripheral projections engaging the "wall of the air duct. A small amount of air leakage is thus allowed between the flared portion l3 and the air duct as indicated by the arrows in Figure 1, to prevent overheating effects.

It will be noted that the fuel injection nozzle supply pipes I 4 are arranged to enter the chamber laterally, being screened from the air flow by an enclosing fairing [5, so that the nose of the chamber is completely free from unnecessary structure, thus assisting in allowing the combustion chamber to be brought up close to the entry to the air duct and giving the maximum freedom in designing the upstream end of the chamber. It is contemplated that the fuel injection nozzle should be of the spill-controlled type, since this type of injection nozzle has excellent characteristics from the point of view of good atomisation over a wide range of fuel flows and is also capable of fine regulation.

The conical bafiie entering at 9 and has at least one port or set of ports 16 at or near its apex in order to introduce to a radially inner region at the base of the fuel jet or spray a pilot supply of combustion air insufflcient to cause reversal thereof whilst further ports l7, 18, respectively are provided at intervals towards the base of the cone to provide a pilot supply of air to a radially inner intermediate region of the jet or spray and also to the radially outer part of the fuel jet spray at a region where, as indicated by the arrows in Figure 1, flow reversal thereof will take place in use due to the air flow.

The major primary supply of combustion air enters through a set of ports [9 at or near the outlet from the annular diffusion passage II (that is at about the shoulder of the flame tube) this supply of air, it will be noted, is so arranged in the region of the fuel jet or spray as to introduce air enveloping the latter somewhat downstream of its region of flow reversal. Further sets of ports 20, 2| for the inlet of secondary combustion air and of cooling or diluent air respectively are provided at spaced downstream zones of the combustion chambers.

The constructions illustrated in the Figures 1 and 2 respectively differ mainly in the arrangement of the ports l6, l1, H3, in the conical bafile 5, and in the arrangement of the ports I9, 20, 2|, in the flame tube, which are self-evident from the drawing. It will be noted also that the diluent air is introduced in the case of Figure 2 through scoop-type elements 22. These have the advantage of introducing the mixing air with less pressure loss than the simple ports of Figure 1 but naturally involve somewhat greater manufacturing complication.

The nature of the flow path of air and fuel in the two cases is similar and is indicated by the arrows in Figure 1; summarising, it will be noted that first the flow is divided immediately on entry to the duct I, a major proportion being by-passed through the diffuser channel ll around the upstream limiting region of the primary combustion zone, and there being a major inflow of primary air for combustion at I 9, with secondary inflows at 20, 2 I, which complete the combustion and effect dilution and mixing of the combustion gases with cooler air to reduce the temperature to a level and degree of uniformity acceptable for operation of a turbine. A minor or pilot flow of air is diffused while entering the cone through the inlet 9 to be fed to the interior and reversal region of the fuel jet or spray. The latter, due to the air flow, reverses in the upstream limiting 5 forms a diffuser for air region of the combustion chamber, whilst due to the bafiiing effect of the chamber construction there is a recirculation of hot gases to the root of the fuel jet.

The constructions illustrated are intended to be used in a gas turbine power plant in which several identical combustion units are disposed annularly about the common axis of a compressor and turbine, but it will be evident that the duct could be of annular form with a plurality of flame tubes disposed around its annulus, the parts again being mutually formed to provide a diffusion channel corresponding to the passage II. An example of this type of construction is shown in Figures 3 and 4 wherein an annular duct 23 is provided with a plurality of flame tubes 24 disposed in circumferentially spaced relation within the duct. The spatial relationships between the fiame tubes 24 and the annular duct 23 are such that a diffusion channel 257is provided which is similar in function to the diffusion channel II. The remaining parts in Figures 3 and 4 correspond to the disclosure of Figure 1 except that the turbine and compressor are more fully illustrated.

Throughout the specification the term diffusion is used to express a zone in which kinetic energy is converted to pressure energy and in which the gas is decelerated without energy loss.

I claim:

1. Combustion apparatus comprising means for supplying a combustion supporting gas flow including a compressor, a duct directly connected to the output of said compressor for receiving the output of said supply means and conveying it in a common general direction, means for injecting fuel in an upstream direction within said duct, the flow of injected fuel being reversed by the gas flow, and structure defining within the duct at least one passage for by-passing gas past the region of fuel reversal, each such passage increas ing in cross-sectional area in the downstream direction to provide for diffusion of all the gas bypassing said region.

2. Combustion apparatus comprising means for supplying a combustion supporting gas flow including a compressor, a duct directly connected to the output of said compressor for receiving the output of said supply means and conveying it in a common general direction, a combustion chamber within said duct, means for injecting fuel in an upstream direction in said chamber adjacent its upstream end, inlet means in said chamber upstream of said fuel injection means for admitting gas to reverse the flow of injected fuel, at least one passage defined within the duct but without the chamber for by-passing gas past the region of fuel reversal, each such passage increasing in cross-sectional area in the downstream direction to provide for diffusion of all the gas by-passing said region and further inlet means in said chamber for admitting by-passed gas therethrough.

3. In a combination gas turbine power plant I having a compressor, a turbine coaxial with said compressor, ducting annularly disposed coaxially of said compressor and turbine and conducting the output from the former to the latter in a common general direction, a plurality of combustion chambers arranged in annular series within said ducting and each defining a zone of at least initial the ducting in each chamber, each chamber having inlet means upstream of said fuel injecting means aamitting part of the compressor output ."to reverse the .fiow of injected tuel, the improve- :ment that comprises the provision 13f :a cdifinser system between said ducting and chambers incorporating at least one .gas flow passage bypassing the region .ofareuersai of ifiuelfkow in Gaelic-chamher :having inlet means its upstream end for admitting at least part :of the compressor butnut, :and outlet means at its downstizeam :end tier x1eliver .of same into a .continuation :if the ducting downstream of SBJIdQI'Bgi'OHRDf iuel reversal, each such passage increasing morass-sectional anea in the downstream direction so as to .efiect under :conditionsof zoperation (controlled :difiusion of;a11 the gas bypassing said region of iuel reversalin each chamber.

4.1a combustion apparatus comprising means -for supplying -.a combustion supporting 'gas flow including a compressor, a zrluctedirectly connected 'to the output of saidmompressor .for receiving :the output of said supply means :andconveying it :in a common generall direction, a combustion cham- -ber within said duct, means for injeoting'iuel -in =an upstream-direc on inisaidichamber adjacent its upstream end, inlet means in lsaid chamber upstream -:of {said :fiuel inie tiona ens z r admitting gas :to reverse the-flew 10f iuject cl :fiueL sai combustion chamber :a- ,d nuct together defining at least one passage for by-passing gas mast ithe gas'by-passing said region.

BETEB FREDERICK ASHWQQD.

References Cited in the file .Of this patent UNITED STATES PATENTS Number Name Date 9721504 Br0Wn --c v- Oct. 11,, 1910 1542294 Foglei V June 16, 1. 5 2164 1 2 Walker June 2 93 2 5 35 Whittle A July 1 3.33% 2593,006 Stalker "Apr. @1950 2,526,122 Darlington Oct. 17,1950 2,529,506 Lloyd et 91. V Nov. 14,1950 '2;556;161 Bailey et a1. Pvt-Fm June12, 19.51

FQREIGN PATENTS Number -Country Date 58%;5'72 Great Britain May; 28, 1947 

